Lots of techniques for effectively compressing a moving picture signal while maintaining the quality of an image have been proposed. In particular, an inter-prediction coding method, that is, a method of extracting a block similar to a current block from a previous picture and coding a difference between the extracted block and the current block, is one of the most effective methods in compressing an image.
In the case of the inter-prediction coding method, however, motion information corresponding to each block must be additionally transmitted instead of coding a residual block and transmitting the coded residual block. For this reason, another image compression method is to reduce the amount of data by effectively coding motion information.
As the size of a prediction block and the number of pictures to be referred become diverse, the amount of data of a residual block is reduced, whereas the amount of motion information to be transmitted (e.g., a motion vector and a reference picture index) is gradually increased.
Accordingly, there is a need for an apparatus capable of reducing the amount of motion information to be transmitted more effectively.